Not Applicable.
The invention relates to the novel thermoplastic materials and impact-modified plastics produced by blending recycled rubber with thermoplastics.
In recent years, there has been substantial progress in the recycling of polymeric materials. Particularly noteworthy has been the development of the Plastic Container Code System used by consumers and community groups to identify, separate, and recycle thermoplastic materials. Unfortunately, progress in the area of recycling thermosetting polymers, such as rubbers, has not been as successful, since these materials cannot be reformed once they have been crosslinked. As a result, other methods to recycle the rubber must be found. Grinding is one method to recycle a thermoset. The ground rubber can be used alone or mixed with thermoplastics to achieve the desired properties, such as impact modification.
The disposal or attempted disposal of non-recycled materials has become a problem in recent years. Numerous environmental hazards are posed by scrap rubbers. For example, scrap tires present self-sustaining fire hazards, and as rubbers such as tires burn, they release toxic compounds into the atmosphere. Rubber piles and dumps are also considered to be a breeding ground for disease-carrying pests.
The market for thermoplastic elastomers has grown dramatically because of the ability to recycle and process these materials using conventional thermoplastics processing equipment. The unique characteristics of thermoplastic elastomers make them an attractive alternative to conventional elastomers in a variety of markets, such as the automotive industry. Consequently, conversion of a conventional elastomer (thermoset) into a thermoplastic elastomer through blending with thermoplastics has the potential to introduce new market applications for scrap rubber.
Some researchers have focused research efforts in this area. For example, Pittolo et al, Rubber Chem. Technol. 58, p.97 (1985), have studied the effect of scrap rubber in polystyrene (PS) to increase impact strength. Their preliminary investigations indicated that recycled rubber crumb acts as a toughening agent for the brittle thermoplastic. The toughness of the resultant materials increased with the degree of rubber/matrix adhesion and decreased with rubber particle size. However, this limits the consumption of scrap rubber in applications because no more than 20% of rubber is typically used in the blends. Other researchers, see McKirahan et al, ANTEC ""96, p. 3110, have studied blends of high-density polyethylene (HDPE) with recycled tire rubber. It was found that tensile strength and hardness decreased with greater rubber concentrations, and ductility improved above 5% rubber content. Data were reported only for rubber concentrations up to 30%. Chidambaram et al, ANTEC ""94, p. 2927, studied the effect of surface treatment of rubber particles on reactive blending with poly(methylmethacrylate) and found that enhanced mechanical properties were possible.
Despite the aforementioned research, there remains a need to encourage recycling and to improve the quality and properties of recycled materials.
Materials ranging from impact-modified thermoplastics to thermoplastic elastomers (TPE) can be obtained from blends of recycled thermoset rubber with thermoplastic polymers by varying the ratio of components in the blend, or by changing the components themselves. The rubber component may include carbon black, or other fillers and additives, and it may be selected from among a variety of thermoset rubbers, both natural and synthetic. The thermoset rubber component can be obtained from a rubber material recycled according to a variety of known techniques. The thermoplastic component can be virtually any suitable polymer, the properties of which can be advantageously modified by combination with a rubber. Polyolefins are among the more preferred thermoplastic components.
In one aspect, the present invention focuses on developing TPE materials from polyolefins (e.g., polypropylene) and recycled ground rubber. The components, particularly the rubber component, are subjected to phase compatibility treatments that are effective to improve the quality of the scrap rubber/plastic blends in response to the structural requirements of several potential applications. The effect of rubber particle size, melt flow index (MFI) for the thermoplastic component, and weight percent of the constituent fractions are also factors that can contribute to the physical properties of the resultant blends. The melt flow index of the thermoplastic component is one particularly significant variable that influences the mechanical properties of the resultant blends. Through proper selection of the components and phase compatibility techniques, blends are able to be tailored to specific applications.
Among the applications for materials made according to the invention are recreational and athletic surface and flooring materials, industrial flooring and footpaths, anti-static computer mats, mounting pads and shock absorbers, membrane protection, airfield runways and roadway surfaces, shoe soles, carpet underlay, automotive floor mats, mud flaps and molded protection strips, automotive door and window seals, gaskets, landscaping materials, watering systems, pipes and hose materials, and flower pots.